Loudspeaker balancing system

ABSTRACT

A system is provided for setting up a multiple-speaker assembly, such as in a public address system or the like, to equalize loudspeaker output while total load remains matched to amplifier output and with a minimum of adjustment or readjustment.

United States Patent Rose [451 July 18, 1972 [5 1 LOUDSPEAKER BALANCINGSYSTEM 2,110,358 3/1938 Dreisbach 179/1 2,149,637 3/1939 Smith ..l79/1 I1 Nelle" 419 wlllow Grove -1 2,341,706 2/1944 Fields ..171/9sPhiladelphia, Pa. 19118 Primary Examiner-Katlfleen H. Claffy [22] Filed1969 Assistant Examiner-Horst F. Brauner [21] Appl. No.: 879,151Attamey-McClure, Weiser & Millman [57] ABSTRACT l. 79 9 1 ,1 hfiggg; Asystem is provided for setting up a multiple-speaker assembly, such asin a public address system or the like, to equal- [58] field of Search..179/1 AT, 1 DD, 1 GA, 1 GP, ize loudspeaker output while total loadremains matched to 179/1 J, 1 1 1 1 B amplifier output and with aminimum of adjustment or read justment. [56] References Cited 10 Chins,2 Drawing figures UNITED STATES PATENTS 1,537,107 6/1926 Edwards 1 7 9/11 PRI SEC :TRANSFORMlER:

l 3 1 2 FROM? PR1 sEc F I j r TAPS ETRANSFORMER ETAPS :Ei]

PRI l ISEC L iTRANSFORMER TAPS SUPP| MENTAL 1 1 1. 0 A n i X, i l l I If FRI MA RY SECONDARY SWITCHES swncuzs SUPPLEMENTAL SWITC H E S 30/VISUAL AURAL 5 START /MONITOR MONITOR sw 1 T c 11 x5 Patented July 18,1972 3,678,202

RAMP 6m x i T X AMPL|FIER 5 L OUTPUT ,g/ AUD'O A RELAY OSCILLATOR h /2if i; r INPUT RELAY VOICE/MUSIC REPEATER PRI I 355 I R APSTRANSFORMETAPS I l k I 3 T Z i 1 ITRANSFORMERISEC FIG. c r TAPS: TAPS I 1 1 X; t

PRI I ISEC PS|ITRANSFORMER|ITAPS SUPPLEMENTAL l LOAD Br, v I I l 1 mPRIMARY SECONDARY SWITCHES SWITCHES SUPPLEMENTAL SWITCHES I l l 30pVISUAL AuRAL MONITOR MONITOR 25 START SWITCH S 25 I l/VVZ/V/fl f 1NELSON J. ROSE M fia; M's/13 LOUDSIEAKER BALANCING SYSTEM This inventionrelates to balanced installation of audio systems.

In public address or similar audio systems utilizing several or morespeaker locations it becomes increasingly difficult to balance speakeroutput and to match the total load reasonably well to amplifier outputwithout tedious and time-consuming readjustment of speaker transformertaps. The difficulties are accentuated by variation in equipmentcharacteristics and by non-homogeneity in the environment, whetherindoors or outdoors. Mis-estimation of amplifier output requirement maylead to substitution of another amplifier, necessitating tapreadjustment throughout, despite previous relative balance, so as toavoid a resulting mismatch and accompanying sound distortion and/orinadequate sound level.

A primary object of the present invention is provision of an improvedsystem for balancing speaker output in multiplespeaker audioinstallations.

Another object is ready matching of amplifier output and total load insuch installations.

A further object is provision of apparatus for accomplishing theforegoing objects.

Other objects of this invention, together with means and methods forattaining the various objects, will be apparent from the followingdescription and the accompanying diagrams.

FIG. 1 is a largely schematic diagram of certain component apparatusarranged according to this invention; and

FIG. 2 is a largely schematic diagram of other component apparatus soarranged to practice the invention.

In general, the objects of this invention are accomplished in a systemof balancing loudspeaker output for a multiplespeaker installation fedby a given amplifier and wherein speakers at each of a number of speakerlocations are connected thereto through respective transformers whosesecondary windings are connected via appropriate taps to the speakervoice coils with proper impedance matching. As practiced the inventionincludes the steps of monitoring the amplifier output and maintainingthe load therefor essentially constant, monitoring the output sound atany given speaker location and adjusting the transformer primary windingtaps, and further adjusting the secondary taps if required, to provide adesired output sound level. Each adjustment is made while monitoringpreselected voice or music (or both) selections repeatable at will anduniform throughout each repetition. After such procedure has beenfollowed for each and every speaker location an essentially correctsound level should prevail with little or no necessity for tapreadjustment.

FIG. 1 shows schematically certain apparatus components andinterconnection thereof according to this invention. They areconveniently grouped at a single location and may be referred to as thefixed" or home" unit. It will be understood that for installationsoutdoors such unit usually will be grossly movable, as in a panel truck,to the locale of each installation but that once there it need not bemoved to each speaker location, as distinguished from other apparatuscomponents (shown in FIG. 2) that are referred to as the mobile" unitand discussed hereinafter.

As illustrated, the fixed unit includes audio amplifier 10, which hasassociated with it adjustable resistor R as a gain or output control.The amplifier has power input leads from contacts x,x to be connected toan external power line or an internal power supply (not shown). Theamplifier output leads, one of which contains output relay l2 andadjustable load'compensating resistor R go to contacts y,y shown furtherin the succeeding view. The output relay has a shorting connectiondiscussed further below, from input relay 14. The input relay itselfmakes connections to the amplifier to control the signal input thereto.Arranged for alternative connection by the input relay to the amplifierare audio oscillator 16 and voice/music repeater 18, both of which areadapted to provide audio-frequency output thereto and also have powerinput from contacts x,x. The voice/music repeater has an interconnectionfrom the output relay and conveniently takes the form of a tape playerprovided with at least one endless loop of recorded voice or music (orboth) selections to be monitored during installation of the variousspeakers in an audio system. More detailed description of thesecomponents would be superfluous in view of their largely conventionalnature except as noted in discussion of the functioning thereof setforth hereinafter.

FIG. 2 shows schematically apparatus components of the aforementionedmobile unit in conjunction with several speakers by way of example, itbeing apparent that the number of speakers could be increasedpractically indefinitely. Speakers 1, 2, and 3 are connected in parallelto contacts y,y to receive the output from amplifier 10 (shown inFIG. 1) by way of respective transformers X X and X Each transformer hasconventional taps to its primary and secondary windings, indicated asPRI TAPS and SEC TAPS, respectively, at opposite ends within the blocksrepresenting the transformers. Broken lines, with arrows, to therespective winding taps indicate interconnection for tap selection oradjustment by means of two sets of switches shown so connected to thefirst transformer: primary switches Sp to the primary taps and secondaryswitches S SEC to the secondary taps thereof.

Two large vertical arrows in FIG. 2 terminate a pair of leads juxtaposedto the lines from contacts y,y to indicate ready connection thereto anddisconnection therefrom, which normally takes place at or near eachspeaker transformer location as will be further apparent from thefunctional discussion hereinafter. Shown so connected in parallel acrossthis pair of leads are supplemental load 21, having supplementalswitches S associated therewith as indicated by the interconnectingbroken line and arrow, start switch (button) S visual monitor 23 inseries with adjustable resistor R and aural monitor 25 in series withadjustable attenuator R The supplemental load includes numerous fixedresistors variously connectable by means of the supplemental switches,conveniently multiple-paralleled and calibrated in watts, to set thetotal load including any connected speakers essentially equal to theamplifier power output, as mentioned further in the functionaldescription hereinafter. The primary switches, also convenientlycalibrated in watts, are connected to the taps of the primary winding ofthe transformer for any given speaker being balanced to permit selectionof whatever portion of that primary winding will provide proper speakeroutput. The secondary switches, which are conveniently calibrated inohms, are connected to the taps of the transformer secondary winding topermit selection of whatever portion of the secondary winding will matchthe speaker impedance.

The primary and secondary switches are preferably of rotary type orautonomous self-cancelling bank type (break before make). The visualindicator preferably comprises a highimpedance (negligible loading)highly ballistic meter move ment with good frequency response over arange of at least'50 to 8,000 hertz and with an indicator scaled inkeeping with transformer primary notation, such as 0 to 100v. for a 70v.line. The aural monitor preferably comprises high-fidelity bridgingearphones of circumaural type to negate ambient noise masking. Bothmonitors facilitate checking on the amplifier output: visually foramplitude output and aurally for undistorted output per type of voice ormusic input.

Operation of this system to practice the present invention will bereadily understood from the foregoing description of the apparatuscomponents and interconnection thereof and the following proceduralexplanation directed particularly to a first speaker and itstransformer. It is assumed that the audio amplifiers gain has beenproperly set internally, as by adjustment of R to deliver its ratedwattage or required portion thereof, e.g., watts, at appropriateconstant voltage, such as the conventional 70.7v. If no speaker is yetconnected the supplemental load is the total load and is set bydepression of the appropriate supplemental switch(es) in the amount ofthe amplifier rated wattage. At this stage the system is in standbymode, with the'audio oscillator (as standby audio means) providing aninput to the amplifier via normally closed contacts of the input relay,but with the output being insufficient to actuate the output relay.Depression of the appropriate secondary switch(es) matches thetransformer secondary winding impedance to that of the speaker voicecoil, usually 4 ohms or an even multiple thereof. Then the installer oroperator estimates the desired wattage of the speaker and depresses thecorresponding primary switch(es) to complete the circuit from theamplifier to the speaker.

After making tentative or trial connections to a speaker as justsummarized, the operator presses the start switch button, which shortsout such load entirely (i.e., effectively shorting contacts y,ytogether) so that the entire output voltage appears across Rmomentarily, thereby actuating it the output relay. The closing of theoutput relay applies power from x,x to the tape transport motor (orequivalent means) of the voice/ music repeater, and by way thereof theinput relay, actuating both. Actuation of the input relay opens itsnormally closed contacts, thereby removing the audio oscillator outputas the amplifier input, and closes normally open contacts to substituteas such input the output of the voice/music repeater. The input relayalso closes a pair of normally open contacts flanking the output relay(and parallel resistor R thereby shorting them out of the amplifieroutput line, whereupon full amplifier power is developed across theintended load.

Notwithstanding release of the start button, the input relay holds untilcompletion of the voice/music tape transmission, thereby providing apreselected period of time, such as from about one-fourth to one-halfminute, for primary tap adjustment by means of the primary switches. Theholding action, conveniently provided by the tape transport motorpotential, is broken at the end of a complete voice/music transmissioncycle in any suitable manner, as by presence of a conductive strip atthe endpoint on the tape loop, which deenergizes the tape-transportmotor and, thus, the input relay. This removes the short in one of theamplifier output leads, to restore the output relay and parallelresistor R therein, and restores the audio oscillator to the amplifierinput, whereupon the system is back in the standby mode.

Whenever the start button is next depressed the entire cycle justdescribed will repeat itself. If the operator has completed adjustmentof the first speaker satisfactorily, he wires into the circuit the tapsso selected and moves the mobile unit on to the next speaker and repeatsthe procedure with its transformer, and so on. As each speaker is addedto the line, the operator readjusts the supplemental switch(es) so as tosubtract from the setting thereof the wattage load represented by theprimary switch setting of the newly connected speaker, as well as theprevious speaker loads. Of course, the voice/music repeater may berecycled as often as desired at any single location, until the operatoris satisfied with the speaker output at that location. Similarly theoperator can return to a previously adjusted speaker transformer andcycle the voice/music transmission to recheck that speaker and toreadjust the transformer taps, as may be necessitated by environmentalchanges, for example.

Notwithstanding description and illustration of a preferred embodimentof this invention hereinabove, various modifications may be madetherein, as by adding, combining, or subdividing parts or steps, whilemaintaining at least some of the advantages and benefits of theinvention. The invention itself is defined in the following claims.

The claimed invention is:

1. ln a system of balancing loudspeaker output for a multiple-speakerinstallation fed by a given amplifier and wherein speakers at each of anumber of speaker locations are connected thereto through respectivetransformers whose primary'windings are connected via appropriate tapsto the amplifier output and whose secondary windings are connected viaappropriate taps to the speaker voice coils with proper impedancematching, the improvement comprising monitoring the amplifier output andmaintaining the load therefor essentlally constant, monitoring the soundoutput at any given speaker location, and adjusting winding taps of thetransformer to provide a desired output sound level.

2. Speaker balancing system according to claim 1, including the step ofproviding a repeatable audio transmission having known characteristicsto the speakers during such adjustment.

3. Speaker balancing system according to claim 2, wherein the amplifieroutput is providedwith a supplemental load, which together with the loadprovided by the speakers equals the rated amplifier output, andincluding the step of readjusting the supplemental load to compensatefor each change in load occasioned by any change in speaker connections.

4. In a system of balancing loudspeaker output for a multiple speakerinstallation, wherein sound output at each of a plurality of speakerlocations is monitored aurally during adjustment of speaker transformertaps, the improvement comprising providing a repeatable voice/musictransmission to be so monitored during such adjustment, and includingthe step of providing a standby output to the amplifier when therepeatable voice/music transmission is absent, the resulting amplifieroutput being adapted to effect substitution of the repeatablevoice/music transmission as the amplifier input upon momentary shortingout the speaker load.

5. Speaker balancing system according to Claim 4, including the steps ofswitching manually from the standby input to the repeatable voice/musictransmission and switching automatically to the standby input after eachrepetition of the voice/music transmission.

6. ln a loudspeaker balancing system for an audio installation havingspeakers at a plurality of locations and multitapped audio transformersfor use therewith, the combination of an audio amplifying means havingan output line across which the tapped primary windings of the speakertransformers are connectable in parallel as the principal load, thesecondary windings of the transformers being connected with properimpedance matching to voice coils of the speakers, calibrated audioinput means operatively connected to the amplifying means and adapted toprovide thereto a repeatable audio transmission having knowncharacteristics, supplemental load means for connection across theoutput line, and switch means for varying the transformer windingconnections and for varying such connection of the supplemental load,including output relay means connected in series in the output line,shorting switch means across the output line at a location between theoutput relay means and any load across the line, the output relay beingresponsive to shorting of the output line by the shorting switch meansand effective to actuate the audio input means.

7. Speaker balancing system according to Claim 6, including standbyaudio input means, input relay means normally connecting the standbyaudio input means to the input of the amplifying means and responsive toactuation of the calibrated audio input means to disconnect the standbyaudio input means therefrom and connect the calibrated audio input meansthereto until completion of the repeatable audio trans mission.

8. Speaker balancing system according to claim 7, wherein the inputrelay means also is adapted to short the output line around the outputrelay means.

9. Speaker balancing system according to claim 7, wherein the inputrelay means is adapted to remain in actuated condition regardless ofdiscontinuation of the short across the output line by the shortingswitch means and release of the output relay means.

10. Speaker balancing system according to claim 9, wherein thecalibrated audio input means is adapted to deactivate the holding relaymeans upon completion of one complete transmission of the audio signalstherefrom.

* k it i

1. In a system of balancing loudspeaker output for a multiplespeakerinstallation fed by a given amplifier and wherein speakers at each of anumber of speaker locations are connected thereto through respectivetransformers whose primary windings are connected via appropriate tapsto the amplifier output and whose secondary windings are connected viaappropriate taps to the speaker voice coils with proper impedancematching, the improvement comprising monitoring the amplifier output andmaintaining the load therefor essentially constant, monitoring the soundoutput at any given speaker location, and adjusting winding taps of thetransformer to provide a desired output sound level.
 2. Speakerbalancing system according to claim 1, including the step of providing arepeatable audio transmission having known characteristics to thespeakers during such adjustment.
 3. Speaker balancing system accordingto claim 2, wherein the amplifier output is provided with a supplementalload, which together with the load provided by the speakers equals therated amplifier output, and including the step of readjusting thesupplemental load to compensate for each change in load occasioned byany change in speaker connections.
 4. In a system of balancingloudspeaker output for a multiple speaker installation, wherein soundoutput at each of a plurality of speaker locations is monitored aurallyduring adjustment of speaker transformer taps, the improvementcomprising providing a repeatable voice/music transmission to be somonitored during such adjustment, and including the step of providing astandby output to the amplifier when the repeatable voice/musictransmission is absent, the resulting amplifier output being adapted toeffect substitution of the repeatable voice/music transmission as theamplifier input upon momentary shorting out the speaker load.
 5. Speakerbalancing system according to Claim 4, including the steps of switchingmanually from the standby input to the repeatable voice/musictransmission and switching automatically to the standby input after eachrepetition of the voice/music transmission.
 6. In a loudspeakerbalancing system for an audio installation having speakers at aplurality of locations and multi-tapped audio transformers for usetherewith, the combination of an audio amplifying means having an outputline across which the tapped primary windings of the speakertransformers are connectable in parallel as the principal load, thesecondary windings of the transformers being connected with properimpedance matching to voice coils of the speakers, calibrated audioinput means operatively connected to the amplifying means and adapted toprovide thereto a repeatable audio transmission having knowncharacteristics, supplemental load means for connection across theoutput line, and switch means for varying the traNsformer windingconnections and for varying such connection of the supplemental load,including output relay means connected in series in the output line,shorting switch means across the output line at a location between theoutput relay means and any load across the line, the output relay beingresponsive to shorting of the output line by the shorting switch meansand effective to actuate the audio input means.
 7. Speaker balancingsystem according to Claim 6, including standby audio input means, inputrelay means normally connecting the standby audio input means to theinput of the amplifying means and responsive to actuation of thecalibrated audio input means to disconnect the standby audio input meanstherefrom and connect the calibrated audio input means thereto untilcompletion of the repeatable audio transmission.
 8. Speaker balancingsystem according to claim 7, wherein the input relay means also isadapted to short the output line around the output relay means. 9.Speaker balancing system according to claim 7, wherein the input relaymeans is adapted to remain in actuated condition regardless ofdiscontinuation of the short across the output line by the shortingswitch means and release of the output relay means.
 10. Speakerbalancing system according to claim 9, wherein the calibrated audioinput means is adapted to deactivate the holding relay means uponcompletion of one complete transmission of the audio signals therefrom.